Skyline logging processes, used extensively in mountainous or hilly logging operations, require effective operation of a log skidding carriage for playing out and retracting a drag line while a movable carriage is suspended on a skyline. The skyline is stretched between two supports in an inclined direction. The log skidding carriage travels along the skyline to carry logs along its length. The dragline is controlled by a reel at the upper end of the skyline system. The dragline is reeled in to pull the carriage uphill and reeled out as the carriage moves downhill due to gravity. It is also reeled in or out while the carriage is locked in a stationary position on the skyline to move logs attached to the dragline toward or away from the carriage.
Logs are moved along a skyline system by attaching one or more logs to the dragline. The dragline is then used to raise the logs up to the carriage, which can then be moved uphill or downhill to a landing where the logs are lowered and released by operation of the dragline.
To operate a log skidding carriage of this nature, one must control operation of the dragline reel and a pair of alternately engageable clamps that sequentially lock either the skyline or the dragline relative to the log skidding carriage. An example of a mechanical clamping system for this purpose is disclosed in U.S. Pat. No. 3,948,398, issued Apr. 6, 1976 to Christensen. An example of a radio controlled carriage is shown in U.S. Pat. No. 4,515,281, issued May 7, 1985 to Maki. Each of these patents describes skyline logging operations in greater detail, and no further elaboration of this well-known system is believed necessary to an understanding of the present invention.
The development of skyline logging systems has led to increased demand for radio controlled log skidding carriages, which provide greater versatility to the carriage operation by making it possible to stop the carriage at any location along the skyline. However, prior carriages of this nature have utilized separate clamp mechanisms for the skyline and dragline, as exemplified in the disclosure of U.S. Pat. No. 4,515,281. The present invention was developed in an effort to simplify the mechanisms of a radio controlled carriage, while also providing a mechanical interlock in each of the required cable clamps. This safety feature assures that a clamp, once locked about a cable, will not be released due to subsequent failure of associated hydraulic systems.